The accelerometer disclosed in French patent No. FR 2 558 263 may be cited as one example of this kind of microstructure. The accelerometer comprises, within a thin layer, a first portion cut out from said thin layer and a second portion consisting of the remainder of the thin layer, the first portion being connected to the second by means of flexible beams allowing this first portion, called the “sensitive” portion, to move with a certain amplitude in the plane of the thin layer. This device is used to measure the accelerations of any system to which it is attached, by means of an electrical capacitance variation caused by said movement.
To minimize the cost of microtechnology fabrication of this kind of accelerometer, it is necessary for the basic die to have as small a surface area as possible. This implies that said sensitive portion, which serves as a seismic mass, is very small (its mass is conventionally of the order of 1 mg). Moreover, the space around it is evacuated to eliminate collisions with air molecules, which would cause unwanted accelerations of the seismic mass that would become more and more of a problem as the seismic mass became smaller and smaller.
In the case of this kind of microcomponent, and many others, it is therefore necessary to be able to maintain a vacuum in an enclosure formed within the microstructure and within which the microcomponent is placed. In the context of the invention, it will be assumed that at least two “substrates” each containing a wall portion of said enclosure are assembled together to form the microstructure or a portion of the microstructure.